POLAND_SPUD wrote:rag I think that it would be really great if you could add a simple Cd calculator to this.... Cd is just way too important for ballistics... it's possibly the least known variable for all of us
Well, a Cd calculator is quite a difficult thing. However, there is going to be a table of Drag coefficients for common shapes, and given that similar shapes tend to have sufficently similar drag coefficients for our purposes, that should easily cover most situations.
iknowmy3tables wrote:cool launch program, only if there were a chamber pressure variable.
This is an external ballistics calculator, not an internal ballistics one.
For now, it's designed to work hand in hand with GGDT and EVBEC, with a muzzle velocity calculated in another program - or rather better, actually measured in real life - and calculate a range from that information, rather than have me bite off more than I can chew.
Not to say I'll never make an internal ballistics tool, but for now, GGDT does a very good job of that under most circumstances - the obvious exception being discussed below.
@bigbob12345: Not a typo, but another mistake I'm afraid.
GGDT is known to give rather... generous, shall we say... results for projectiles that reach or exceed the sound barrier.
It's hard to break the speed of sound in a gas, and impossible to break the particle speed. In air, the speed of sound is around 1120 fps, depending on temperature, humidity, and other factors.
You need a lot of brute force for the job, and therefore, air powered cannons, even one using pressures of 300 or 400 psi, have severe trouble breaking 1000 fps.
Getting to around 1100 is near impossible (although JSR did once manage it), and going past that is going to get even harder.
As the average particle speed in air is somewhere between 1600 and 1700 fps depending on the temperature, and it's not actually possible for a gas, regardless of it's pressure, to accelerate something past it's particle speed... which makes the 1900 fps figure you have completely erroneous.
As the particle speed is approached, you lose effective pressure, and thus acceleration, which makes it hard to even get to 75% of the particle speed (and that will only happen after you've dealt with the first opponent of the sound barrier)
1200 fps might just be achievable with high pressures, a light projectile, a low friction barrel and a REALLY powerful valve.
But given the trouble with the sound barrier, seldom will I believe a velocity claim of more than about 90% of the SOS from GGDT, and even then I normally just round back down to around 90%.
In your case, I think you should be happy with achieving over 900 fps with 100 psi, regardless of barrel length. Getting over 1000 fps is the region of brute force cannons using 3 or 4 times that pressure.
However, with helium, 2800 fps is potentially achievable, as that's not
much over 90% of the SOS in helium (around 3000 fps) - but you'll still need more than 100 psi.
You should also bear in mind, if you're using CO2 in your KAMG, that's going to blunt performance even more than with air. The speed of sound in CO2 (at room temperature, let alone when cooled) is only 900 fps, and based on the gas dynamics of CO2, you're not going be be capable of getting half as close to the sound barrier in air as an air powered launcher is capable of.
CO2 is not a gas that's suitable for breaking the sound barrier.
but where will we find break line that long? hehe 
